Inkjet printers employing Memjet® technology are commercially available for a number of different printing formats, including small-office-home-office (“SOHO”) printers, label printers, digital inkjet presses and wideformat printers. Memjet® printers typically comprise one or more stationary inkjet printheads, which are user-replaceable. For example, a desktop printer may comprise a single user-replaceable multi-colored or monochrome printhead, a high-speed digital press may comprise a plurality of user-replaceable monochrome printheads aligned along a media feed direction, and a wideformat printer may comprise a plurality of user-replaceable printheads in a staggered overlapping arrangement so as to span across a wideformat pagewidth.
Ink is supplied to an inkjet printhead via an ink delivery system, which is designed primarily for delivering ink to the printhead at a predetermined hydrostatic pressure. Ink delivery systems also typically include an ink filter for filtering particulates from the ink. The ink filter may comprise any suitable filter material housed in a chamber having an inlet and an outlet.
Air bubbles are a perennial problem in inkjet printers. Air bubbles that reach inkjet nozzles can block nozzles and cause catastrophic deprime events. Air bubbles can also reduce the efficacy of ink filters in the ink delivery system by blocking microscopic pores in the filter material.
To some extent, the problems associated with air bubbles can be mitigated through the use of degassed ink in a closed ink delivery system. However, such ink delivery systems are not immune to the problems of air bubbles even when degassed ink is employed. For example, air may be intentionally introduced into the ink delivery system via printhead depriming operations when air is drawn through the printhead so that the printhead can be replaced. This introduced air can circulate around the ink delivery system and become trapped in the ink filter, thereby reducing the efficacy of the ink filter and adversely affecting print quality. If the ink filter becomes catastrophically blocked with air bubbles, it will require replacement by the user which is both inconvenient and time-consuming.
In some ink delivery systems described in the prior art, the ink filter is connected to a de-aeration pump, which removes air from the filter chamber housing the filter material. The de-aeration pump ensures that any air bubbles trapped in the ink filter can escape to atmosphere without causing long-term problems through continuous build-up of air bubbles. However, de-aeration pumps add to the cost and complexity of ink delivery systems.
It would therefore be desirable to provide an ink filter, which enables removal of air bubbles without relying on a de-aeration pump.